LILLEY, T. R.*; MEDLER, S. ; MYKLES, D.L.; Colorado State University; University at Buffalo; Colorado State University: Variable expression of myofibrillar protein isoforms in juvenile lobster claw muscles

Adult lobsters (Homarus americanus) possess two types of claws: cutter claws (CT) and crusher claws (CR). Adult CT claws contain mostly fast-twitch fibers and CR claws contain all slow-twitch fibers. These two fiber types are distinguished by different assemblages of myofibrillar protein isoforms. Fast fibers are identified by the expression of P75 and high levels of troponin-I₁ (TnI₁), while slow fibers express primarily TnI₃ and do not express P75. Juvenile lobsters initially have identical claws, but these gradually differentiate into the dimorphic claws of adults over subsequent molt cycles. During this process fibers undergo a transformation in which CT fibers gain their fast properties and CR fibers gain their slow properties. In the current study, we analyzed the presence of P75 and TnI proteins in juvenile claw muscles. The goal was to determine how the expression of P75 and TnI in individual juvenile fibers differs from adult fibers. Protein expression was measured by SDS-PAGE and Western blotting. Unlike adult claws, juvenile claws contained fibers expressing high levels of P75 as well as uniformly high levels of TnI₁, TnI₂, TnI₃, and TnI₄. During development, they began to differentiate into their respective claw types. The juvenile CT claw fibers began to express high levels of TnI₁ and retained some expression of TnI₂ and TnI₃. As expected, the CT claws also continued to express P75. The juvenile CR claw fibers began to express high levels of TnI₃ and continued to express lower levels of TnI₁ and TnI₂. Interestingly, P75 continued to be expressed in the juvenile CR. These data suggest that P75 and TnI expression is more variable in juvenile claws, and that this expression becomes more defined as juveniles reach adulthood. Supported by NSF (IBN-0077422) and NIH (AR08597-01A1).